X-ray diagnostic apparatus

ABSTRACT

An X-ray diagnostic apparatus includes an X-ray generating unit which generates X rays, an X-ray detecting unit which detects X rays transmitted through a subject, an X-ray exposure operating unit which is operated by an operator, and a system control unit which controls the X-ray generating unit in order to start the generation of the X rays from the X-ray generating unit at a time point when a heart rate phase of the subject reaches a specified phase after the X-ray exposure operating unit is operated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2007-094689, filed Mar. 30, 2007,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an X-ray diagnostic apparatus whichcopes with contrast study of a heart or the like.

2. Description of the Related Art

In X-ray contrast study of hearts and intervention, it is very importantto understand shapes and functions of blood vessels and hearts. However,since cardiac movement cannot be avoided differently from the otherregions of bodies, projection data is mainly used for the understandingof the hearts.

In recent years, applications for heart regions are gradually beingdeveloped. They include an application for creating a digitalsubtraction angio (DSA) image of coronary artery, an application foridentifying perfusion from coronary artery to cardiac muscle, anapplication for locally/wholly creating a three-dimensional structure ofcoronary artery, and the like.

In order to create a DSA image of coronary artery, an image which hardlyhas an effect of a contrast agent is required as a satisfactory maskimage for at least one heart rate. In some cases, the timing at whichinjection of contrast agent starts is too early and thus satisfactorymask images for one heart rate cannot be collected. This becomes a fatalproblem for the creation of DSA images. Also when the perfusion fromcoronary artery to cardiac muscle is identified, the similar problemmight arises.

When a three-dimensional structure of coronary artery is locally orwholly created, an image at end-diastole with comparatively lessmovement becomes a key. For example, in a method for paying an attentiononly to a target region and correcting a movement of this region so asto create a local three-dimensional structure, a target region isspecified on an image at end-diastole.

When photographing is started just after the end-diastole passes, thenumber of end-diastoles to be included in an any photographing zonemight be reduced. Since the amount of specifying information is reducedin this case, information is insufficient, and thus restructure is atrisk of being unsatisfactory.

On the other hand, when a three-dimensional structure of coronary arteryis wholly created, the restructure is carried out by using only imagesat end-diastole and less information. In such a method, image quality isgreatly influenced by whether the number of end-diastoles is reduced byone or increased by one.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to collect necessary images ofheart rate phase by means of less radiation dose.

According to a first aspect of the present invention, there is providedan X-ray diagnostic apparatus comprising: an X-ray generating unit whichgenerates X rays; an X-ray detecting unit which detects X raystransmitted through a subject; an X-ray exposure operating unit which isoperated by an operator; and a control unit which controls the X-raygenerating unit so as to start the generation of the X rays from theX-ray generating unit at a time point when a heart rate phase of thesubject reaches a specified phase after the X-ray exposure operatingunit is operated.

According to a second aspect of the present invention, there is providedan X-ray diagnostic apparatus, comprising: an X-ray generating unitwhich generates X rays; an X-ray detecting unit which detects the X raystransmitted through a subject; and a control unit which controls theX-ray generating unit in order to change a pulse width of the X raysaccording to heart rates of the subject.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a diagram illustrating a structure of an X-ray diagnosticapparatus according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a structure relating to a generationportion of an X-ray generation signal in a system control unit of FIG.1;

FIG. 3 is a diagram illustrating timing of the X-ray generation signaland a contrast agent injection signal in the embodiment;

FIG. 4 is a diagram illustrating another timing of the X-ray generationsignal and the contrast agent injection signal in the embodiment;

FIG. 5 is a diagram illustrating a change in a frame rate with respectto a change in heart rate by means of control using the system controlunit in FIG. 1;

FIG. 6 is a diagram illustrating a change in an X-ray pulse width withrespect to the change in the heart rate by means of control using thesystem control unit in FIG. 1;

FIG. 7 is a diagram illustrating another timing of the X-ray generationsignal and the contrast agent injection signal in the embodiment;

FIG. 8 is a diagram illustrating a relationship between a heart ratephase and a cardiac movement;

FIG. 9 is a diagram illustrating a pulse width for low-speed-heart rategraph in the embodiment; and

FIG. 10 is a diagram illustrate a state that the pulse width is changeddynamically according to the heart rate phase in the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings.

In an outline of the embodiment, conventionally photographing is startedat the moment when a photographing start trigger is turned on, but inthis embodiment, moreover, photographing is started at the moment when aheart rate phase reaches a predetermined heart rate phase or before aconstant time from the scheduled time point. As a result, necessaryimages of the heart rate phase are collected without excess anddeficiency. The start of contrast is specified after at least one cyclepasses from the start of photographing. As a result, necessaryinformation (mask images at necessary cycles) can be collected securely.

FIG. 1 illustrates a structure of the X-ray diagnostic apparatus of theembodiment. The X-ray diagnostic apparatus 100 in the embodiment has anX-ray generating unit 1 which generates X rays for irradiating a subject150. The X-ray generating unit 1 has an X-ray tube 15 which generates Xrays, and an X-ray diaphragm device 16 which forms a radiation field ofX rays. A high-voltage generator 42 of a high-voltage generating unit 4applies a high voltage to the X-ray tube 15 under the control of anX-ray control unit 41, and supplies a filament current. As a result, Xrays are generated from the X-ray tube 15. The X-ray tube 15 issupported a C-shaped arm 5 which is supported rotatably to an armrotatable moving mechanism 31 on at least three orthogonal shafts. Aplane detector 21 of an X-ray detecting unit 2 is held to a position anddirection on the C-shaped arm 5 opposed to the X-ray tube 15.

The plane detector 21 has a plurality of semiconductor detectingelements arrayed two-dimensionally, for example. X rays, which transmitthrough the subject 150 placed on a top panel 17 supported movably to atop panel moving mechanism 32 of a bed, are converted into electriccharges by the plurality of semiconductor detecting elements of theplane detector 21 so that the electric charges are accumulated. Theaccumulated electric charges are read as a current signal for eachsemiconductor detecting element or each channel by gate driving of agate driver 22. An electric charge-voltage converter 23 of a projectiondata generating unit 13 converts the current signals read from the planedetector 21 into voltage signals for each semiconductor detectingelement or each channel. An analog-digital (A/D) converter 24 convertsthe voltage signal converted by the electric charge-voltage converter 23into a digital signal for each semiconductor detecting element or eachchannel, so as to output it as image data. An image data storage unit 72of an image data management unit 7 stores image data calculated by rawimage data or an image calculating unit 71. An image display unit 8 hasa display data generating unit 81, a digital-analog (D/A) converter 82and a monitor 83 in order to display image data read from the image datastorage unit 72.

An electrocardiogram collecting unit 6 is attached to the subject 150placed on the top panel 17. The electrocardiogram collecting unit 6 hasa function for measuring an electrocardiogram of the subject 150, and afunction for detecting a specified heart rate phase desired by a doctorbased on the electrocardiography waveform so as to repeatedly generate apulse-shaped cardiography trigger signal. The specified heart rate phasemay be specified by a doctor or the like on free setting or may beautomatically set as a default value for each photographing program andeach photographing mode (analysis type).

The heart rate phase is expressed in such a manner that a period from anR wave to a next R wave is standardized according to percentage and theposition of the period is expressed by percentage. For example, when athree-dimensional structure of coronary artery is created locally orwholly, the heart rate phase corresponding to end-diastole with lessmovement is set as the “specified heart rate phase”. For convenience ofdescription, a cardiography trigger signal is generated when thespecified heart rate phase is 0%, namely, at the timing of an R wave.

A contrast agent injecting device 33 is attached to the subject 150placed on the top panel 17. The contrast agent injecting device 33 iscalled an injector which automatically injects a constant agent to thesubject 150 at timing, injecting amount and an injecting speed which arecontrolled by a contract agent injection signal from the system controlunit 10.

An X-ray exposure button 3 as well as a general operating unit 9 forinputting photographing conditions and the like is connected to thesystem control unit 10. The X-ray exposure button 3 is typically a pushbutton, and while an operator is pressing down the button, an X-rayexposure trigger signal is generated continuously.

As shown in FIG. 2, an X-ray signal generating unit 101, which isconstituted as, for example, a latch circuit in the system control unit10, substantially generates an X-ray generation signal for a X-raycontrol unit 4 continuously for a specified period based on an X-rayexposure trigger signal supplied from the X-ray exposure button 3 and acartographic trigger signal supplied from the electrocardiogramcollecting unit 6. A fall detecting circuit 103 is connected to theX-ray signal generating unit 101. The fall detecting circuit 103 detectsfall of an X-ray exposure trigger signal corresponding to release of apushing-down operation of the X-ray exposure button 3. When the falldetecting circuit 103 detects fall of the X-ray exposure trigger signalor the fall detecting circuit 103 inputs a signal expressing thedetection of the fall of the X-ray exposure trigger signal, the X-raysignal generating unit 101 suspends an X-ray generation signal.

While receiving the X-ray generation signal from the system control unit10, the X-ray control unit 4 continuously supplies a filament current tothe X-ray tube 15 from the high-voltage generator 42, and generates acontrol signal for repeatedly applying a pulse-shaped X-ray tubevoltage. The system control unit 10 generates a control signal forallowing the gate driver 22 to execute an electric charge readingoperation in synchronization with an X-ray generation signal, andgenerates a control signal for allowing the analog-digital converter 24to execute an analog-digital converting operation. With the controlsignals, the X-ray photographing is repeated in a constant cycle duringa specified period for which the X-ray generation signal is generated,and data about a series of a plurality of images are generated.

The system control unit 10 generates a contrast agent injection signalfor the contrast agent injecting device 33 continuously for a perioddifferent from the X-ray generation signal generating period based onthe X-ray exposure trigger signal supplied from the X-ray exposurebutton 3 and the cardiography trigger signal supplied from theelectrocardiogram collecting unit 6. The contrast agent injecting device33 continuously injects a contrast agent into the subject 150 whilereceiving the contrast agent injection signal from the system controlunit 10.

FIG. 3 illustrates a time chart relating to the X-ray exposure operationand the contrast agent injecting operation by means of the systemcontrol unit 10. The cardiography trigger signal which is typicallysynchronous with the R wave is supplied from the electrocardiogramcollecting unit 6 to the system control unit 10 at a stage of an offstate before pushing-down of the X-ray exposure button 3 (on state). Inthis state, the system control unit 10 waits for the supply of the X-rayexposure trigger signal from the X-ray exposure button 3. The supply ofthe X-ray exposure trigger signal is equivalent to a change of the X-rayexposure trigger signal from a standard voltage into a specifiedvoltage. For convenience of description, the supply/suspend of the X-rayexposure trigger signal is described here. Much the same is true on theX-ray generation signal. The X-ray exposure trigger signal is suppliedto the system control unit 10 continuously during a period for which theX-ray exposure button 3 is being pushed down, and the supply of theX-ray trigger signal to the system control unit 10 is suspended during aperiod for which the X-ray exposure button 3 is released.

The system control unit 10 does not generate an X-ray generation signalimmediately at the time point when the X-ray exposure button 3 is pusheddown and the X-ray exposure trigger signal is supplied, but receives theX-ray exposure trigger signal and then stands by until the firstcardiography trigger signal is supplied (queuing time ΔW), so as togenerate the x-ray generation signal. The queuing time ΔW is notprescribed time but fluctuation time according to a period up to a firstR wave after the X-ray exposure button 3 is pushed down. As described,The X-ray generation signal is generated at the time point of the firstR wave after the X-ray exposure button 3 is pushed down. Therefore, evenwhen image data for the period up to the time point of the first R waveafter the X-ray exposure button 3 is pushed down is not necessary fordiagnosis, such useless photographing can be avoided.

As shown in FIG. 4, a certain margin is given to a predetermined heartrate phase, and the photographing may be started slightly earlier byspecified precursor time ΔL than the time point of the first R waveafter the pushing-down of the X-ray exposure button 3, actually, theestimation time point when a R wave whose average cycle passes from aprevious R wave is generated. In this case, the cardiography triggersignal is not a specified phase, but is brought into an on state at thetime earlier by the precursor time ΔL. The precursor time ΔL may bedesigned based on time until blur of the heart rate cycle and collectedimage luminance become stable and time until the rotation at the time ofrotational photographing becomes stable, and is set to 0.33 second, forexample.

The system control unit 10 generates the X-ray exposure trigger signalcontinuously while a device operator is pushing down the X-ray exposurebutton 3, and when the device operator releases the X-ray exposurebutton 3, namely, at the time point when the device operator releasesthe X-ray exposure button 3 regardless of the heart rate phasedifferently from the start of photographing, the X-ray exposure triggersignal is suspended instantly. As a result, the X-ray exposure issuspended immediately, and the photographing is ended.

The injection of the contrast agent is required for a contrast studysuch as DSA of coronary artery. The X-ray exposure button 3 is pusheddown and the X-ray exposure trigger signal is supplied, and then at thetime when a preset second or n-th (n: integer of not less than 3)cartography trigger signal is supplied, the system control unit 10generates the contrast agent injection signal. As a result, theinjection of the contrast agent from the contrast agent injecting device33 to the subject 150 is started. That is, at the time point of thesecond or n-th R wave after the device operator pushes down the X-rayexposure button 3, the injection of the contrast agent is started.Therefore, the photographing is started at the time point of the first Rwave after the device operator pushes down the X-ray exposure button 3,and then the injection of the contrast agent is started with beingdelayed by at least one heart rate period. For this reason, at least oneheart rate period can be secured as a photographing period of a maskimage with few influence of the contrast agent. The heart rate phasewhere the injection of the contrast agent starts is described as the“specified heart rate phase”, namely, the same phase as that of thephotographing start, but another heart rate phase different from the“specified heart rate phase” corresponding to the photographing startmay be set.

The contrast agent may be injected manually instead of using thecontrast agent injecting device 33. In this case, a message that thecontrast agent should be injected, for example, is displayed on thescreen of a display device according to the contrast agent injectionsignal. Also in this case, at the time point of the second or n-th Rwave after the device operator pushes down the X-ray exposure button 3,the device operator is urged to start the injection of the contrastagent. Therefore, the photographing is started at the time point of thefirst R wave after the device operator pushes down the X-ray exposurebutton 3, and then the device operator is urged to start the injectionof the contrast agent by the message with being delayed by at least oneheart rate period.

As shown in FIG. 7, the X-ray signal generation signal is off for apredetermined period ΔW2 after which the contrast agent injection signalis on and the first R wave is generated, and thus the generation of Xrays is suspended. This period is before the contrast agent reaches aphotographing region after it is injected. Applications of imagesphotographed for this period are not much present. When the generationof X rays is suspended for this period, the exposure with X rays can bereduced.

When the X-ray generation signal is on, the system control unit 10counts the number of heart rate cycles after the X-ray generation signalis on by counting the number of the cartography trigger signals. Whenthe counted value reaches a predetermined number of times, the systemcontrol unit 10 does not start the automatic injection of the contrastagent, but may display an injection icon in image display unit forurging the manual injection of the contrast agent. This icon may be amessage. As to the counting of the number of heart rate cycles, a zonefrom R wave to R wave is measured as one cycle, and a zone from thecollection starting to the first R wave is calculated by a ratio of thetime up to R wave to the one heart rate time. When a difference betweenthe predetermined number of times and the number of cycles measured upto R wave is not more than 1, the number of heart rate cycles ismeasured by the ratio of the measured number of cycles up to R wave tothe one heart rate time. The one heart rate time at this time may becalculated by using current heart rate time, or using maximum heart ratetime obtained by multiplying the heart rate time by a constant ratio inorder to take a certain margin into consideration. A certain delay timeis set for the predetermined number of heart rate times, and the iconmay be displayed at timing which is delayed from the predeterminednumber of heart rates. This margin can absorb the blur of the heart ratecycle.

As seen, it is structured such that unless the X-ray exposure triggersignal and the cartography trigger signal are simultaneously in the onstate, the X-ray generation signal is not in the on state. The X-rayexposure trigger signal is in the on state only while the X-ray exposurebutton 3 is being pushed down. The cartography trigger signal is asignal from the electrocardiogram collecting unit 6, and is generatedonly at the time of a predetermined heart rate phase. With such acomparatively simple structure, excess or deficiency of thephotographing in various photographing methods can be effectivelyreduced.

A frame rate during the photographing is described below. As illustratedin FIG. 5, the frame rate representing the number of photographed imagesper second (fps) is dynamically changed according to a fluctuation inthe heart rate by the control of the system control unit 10. The framerate is adjusted by control signals from the system control unit 10 tothe gate driver 22 and A/D converter 24, for example, modulation of aclock signal.

When the heart rate (inverse number of the heart rate cycle) increases,the frame rate is increased gradually, and when the heart rate isreduced, the frame rate is reduced gradually. For example, when theheart rate is not more than 60, the frame rate is set to 15, and whenthe heart rate is over 60 to not more than 90, the frame rate is set to30. When the heart rate is over 90 to not more than 120, the frame rateis set to 45, and when the heart rate is over 120, the frame rate is setto 60.

A pulse width of X rays during the photographing is described. As shownin FIG. 6, the pulse width of an X-ray pulse is dynamically changedaccording to the heart rate by the control of the system control unit10. When the heart rate increases, the pulse width is shortened, andwhen the heart rate reduces, the pulse width is lengthened. For example,when the heart rate is 60, the pulse width is set to 75 msec, and whenthe heart rate increases to 90, the pulse width is shortened to 50 msec.When the heart rate is 120, the pulse width is set to 25 msec.

The pulse width of X rays may be dynamically changed according to theheart rate phase. As shown in FIG. 8, a cardiac movement, for example adistance between two points on a cardiac muscle surface is changedaccording to the heart rate phase. As shown in FIG. 9, the systemcontrol unit 10 holds a pulse width-heart rate flag related to low speedas well as a standard pulse width-heart rate graph. A standard pulsewidth is determined according to the heart rate by using the standardpulse width-heart rate graph. The system control unit 10 determines thepulse width for low-speed according to the heart rate using the pulsewidth for low-speed-heart rate graph. As shown in FIG. 10, the systemcontrol unit 10 alternates the standard pulse width and the pulse widthfor low-speed according to the heart rate phase. When the heart ratephase is included in predetermined (multiple) phase periods, the pulsewidth of X rays is switched from the standard pulse width into the pulsewidth for low-speed. For example, for the period for which the heartrate phase is 10 to 20% and for the period for which it is 50 to 80%,the X rays are set to the pulse width for low-speed longer than thestandard pulse width. For periods other than those, X rays are set tothe standard pulse width shorter than the pulse width for low-speed. Thepulse width is dynamically changed according to the heart rate phase,but the frame rate is also changed dynamically together with the pulsewidth.

The present invention is not limited to the embodiment, and thecomponents can be modified to be embodied without departing from thegist. Further, a plurality of components disclosed in the embodiment issuitably combined so that various inventions can be formed. For example,some components may be deleted from the entire components in theembodiment. Further, components in different embodiments may be suitablycombined.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. An X-ray diagnostic apparatus, comprising: an X-ray generating unitwhich generates X rays; an X-ray detecting unit which detects X raystransmitted through a subject; a contrast agent injection unit whichinjects a contrast agent into the subject; an X-ray exposure operatingunit configured to generate an X-ray exposure trigger signal in responseto an operation by an operator; and an X-ray control unit whichgenerates an X-ray generation signal to start generation of the X raysfrom the X-ray generating unit based on the X-ray exposure triggersignal and a cardiography trigger signal representing a specified phaseon an electrocardiogram of the subject; and a contrast agent injectioncontrol unit which generates a contrast agent injection signal to startinjection of the contrast agent from the contrast agent injection unitbased on the X-ray exposure trigger signal and the cardiography triggersignal, wherein the contrast agent injection signal is generated when apredetermined number of cardiography trigger signals have been generatedafter the generation of the X-ray exposure trigger signal.
 2. The X-raydiagnostic apparatus according to claim 1, wherein the X-ray controlunit generates the X-ray generation signal when the cardiography triggersignal is generated.
 3. The X-ray diagnostic apparatus according toclaim 1, wherein the X-ray control unit stops the generation of the Xrays for a period from a time when the contrast agent injection signalis generated to a time when the cardiograph trigger signal is generated.4. The X-ray diagnostic apparatus according to claim 1, furthercomprising: a control unit configured to control the X-ray generatingunit to generate X-rays during a period which is after the operation ofthe X-ray exposure operation unit and before a heart rate cycle becomesmore stable than a heart rate cycle of the time when the cardiographytrigger signal is generated.
 5. The X-ray diagnostic apparatus accordingto claim 4, wherein the control unit generates the contrast mediuminjection signal when a predetermined number of cardiography triggersignals have been generated after start of the generation of X-rays bythe X-ray generation unit.
 6. The X-ray diagnostic apparatus accordingto claim 1, wherein the control unit generates the X-ray generationsignal when the cardiography trigger signal is generated a first timeafter the X-ray exposure trigger signal is generated.
 7. The X-raydiagnostic apparatus according to claim 4, wherein the control unitstops the generation of the X rays for a period from the a time when asignal relating to the start of injection of the contrast agent to thetime when the cardiography trigger signal is generated.
 8. The X-raydiagnostic apparatus according to claim 1, further comprising a displayunit which displays an icon or a message corresponding to the generationof the contrast agent injection signal.
 9. The X-ray diagnosticapparatus according to claim 1, wherein the X-ray control unit comprisesa latch circuit configured to generate the X-ray generation signal bylatching the X-ray exposure trigger signal and the cardiography triggersignal.